Thanks to the House of Representatives passing the Truth in Caller ID Act of 2010, Caller ID spoofing will be outlawed. Sure, you may prevent your number from being seen, but no more pretending that you're calling from another phone:

It shall be unlawful for any person within the United States, in connection with any real time voice communications service, regard- less of the technology or network utilized, to cause any caller ID service to transmit misleading or inaccurate caller ID information, with the intent to defraud or deceive.

The bill hasn't been written into law just yet—though the Senate has passed its version already—so hurry and get any prank calls out of the way now. [GPO via Ars Technica]